Cardenolides are compounds that can be and are used to treat people suffering from various heart diseases. These materials include digitalis which is a mixture of glycosides and affords on hydrolysis a mixture of the aglycones, for example, digitoxigenin, digoxigenin, gitoxigenin, and many others which are also cardenolides. These substances conform in skeletal structure; with the exception of the placement of hydroxyl groups they all have twenty-three carbon atoms present and are of the cis- decalin type. They are all sterols and are characterized structurally by the presence of a saturated phenanthrene ring system having an additional five membered ring fused thereto. The distinguishing structural features of the cardenolides are the .beta.-oriented hydroxyl group at C.sub.14 and as stated the five-membered .alpha..beta.-unsaturated lactone ring. As indicated above, the compounds are of the cis-decalin type, the angular methyl group and side chain are .beta.-oriented, the B/C ring structure is trans while the C/D structure is cis since C.sub.14 has the .beta. configuration. This is structurally shown in Formula 1. ##STR1## which represents digitoxigenin. Digoxigenin and gitoxigenin have an additional hydroxyl group on the 12-carbon and 16-carbon respectively.
Furyl derivatives of cardenolides have been heretofore obtained by hydride reduction of naturally occurring cardenolides. These derivates obtained from naturally occurring cardenolides have the structure shown in Formula II. ##STR2## Oxidation of these furyl derivatives with peracids or N bromo succinimide respectively yielded selectively lactones of the types III and IV. ##STR3## (J. M. Ferland, Y. Lefebre, R. Deghenghi and K. Wiesner, Tetrahedron Letters, No. 30, 3617 (1966).)
In the above identified U.S. application Ser. No. 080,004 (which is incorporated herein by reference), we have shown that natural cardenolides and cardenolides analogues may be synthesized by a method which features the reaction of an appropriate steriodal ketone with .beta.-furyl lithium and an oxidative and reductive conversion of the furan ring into a five-membered unsaturated lactone.